I want to implement login using facebook in my windows phone 7.1 application
When I try to install Facebook C# SDK using the nuget package manager console. It is added successfully, but when I try to add the reference to my project its giving following error.

I did not write any code or anything. I just want to add the reference to facebook like using facebook; in my code behind file
I just tested this and I cannot reproduce the error.
Make sure you uninstall any old version of the SDK.
Then, right-click the project and add the SDK using nuget.
Do not install by hand.